Factors limiting the success of invasive glossy buckthorn (Frangula alnus) in New Hampshire’s eastern white pine – hardwood forests

Abstract

Glossy buckthorn (Frangula alnus) is an invasive exotic shrub in forests of eastern North America, where it can alter the structure and function of ecosystems. Buckthorn is often abundant in eastern white pine (Pinus strobus) stands, though the specific factors that that allow invasion into these stands are not known. In an observational study, we examined the roles of tree species composition, photosynthetically active radiation (PAR, i.e., sunlight), and soil characteristics in limiting buckthorn success. Data on buckthorn biomass and forest characteristics were collected from 60 locations in closed-canopy pine and hardwood stands in southeastern New Hampshire. Using logistic regression, buckthorn presence was associated with low soil inorganic-N, high PAR, and a deep humus layer. Using generalized linear modeling, buckthorn biomass was positively associated with high PAR and negatively associated with both the basal area of trees other than white pine (non-WP BA) and sand content. The presence of reproductive buckthorn, analyzed with logistic regression, was associated with high PAR and low non-WP BA. Using discriminant analysis, locations with the oldest buckthorn were best predicted by PAR, non-WP BA, sand content, soil inorganic-N concentrations, and humus depth. White pine BA was not a predictor in any chosen model of buckthorn success. Overall, areas with high PAR and low non-WP BA were the strongest predictors of buckthorn success, and thus sites with these characteristics appear most susceptible to invasion.